The embodiments described herein relate to a thermal interface between a heat source and a heat exchanger. More particularly, the embodiments described herein relate to designing a thermal interface to reduce thermal resistance and effectively dissipate heat from the heat source.
A thermal interface material (TIM) is a material employed to reduce thermal resistance at the interface of the heat source and the heat exchanger. The path of heat removal from an electronic package, such as a central processing unit (CPU), involves conduction across the interface of the CPU case surface, through a TIM, into a heat exchanger, such as a heat sink, and then convection to the environment. Thermal resistance is a measure of how well heat is transferred across the interface of two mating rigid surfaces, such as the CPU and the base of a heat sink. The lowest possible interface resistance is reached when the heat sink temperature approaches that of the CPU.
The CPU and heat sink surfaces being joined contain a combination of surface roughness and surface non-flatness. On a macroscopic level, this roughness is non-planar in the form of a concave, convex, or wavy surface, or a combination thereof across the surface. This roughness results in the interface being separated by air filled gaps without the presence of TIM. Contact resistance may be reduced by increasing the area of contact spots and using a TIM of high thermal conductivity that can conform to the imperfect surface features of the mating surfaces.